This invention relates to data processing systems. More particularly, the invention relates to a well-logging data acquisition and data processing system for obtaining well-site measurements from logging tools traversing a well borehole, and for producing well-site logs in virtually real time.
A typical prior-art computer-controlled well-logging data acquisition and data processing system will include a large number of peripheral devices with which the host computer exchanges data. A large number of peripheral units are present in prior-art well-site data processing systems in order for the host computer to concurrently perform its multiple functions of gathering measurements of the signals coming from one or more logging tools traversing a well borehole, and the processing of these measurements to obtain and present logs of different well parameters in as near real time as possible. Included in these peripheral units is a tool interface for interfacing each type of logging tool which is traversing the well borehole to the environment of the data processing system. Peripheral units, such as magnetic tape units, disc memory units, keyboard hard copy printers, CRT graphic displays, strip chart recorders, etc., are typically required in order for well-logging data processing operations to be possible at the well-site.
These prior-art well-site data processing systems typically connect each of these peripherals to the host computer for communications therebetween over a single data bus. In a well-loging environment, this architecture has several disadvantages. The large number of separate peripheral units requires the interconnecting data bus to be excessively long. This excessive length reduces the speed at which signals can propagate along the bus, and tends to degrade the quality of the bus signals themselves. A failure in the bus results in the entire system being shut down, even where back-up redundant host computers are provided. These back-up computers must also communicate with the peripherals over the same bus as the host computer.
Another disadvantage present in prior-art well-site data processing systems having the single peripheral-to-processor communication link is the excessive software overhead required for the host computer to handle the input/output data transfers between processor and peripherals. For the host computer to perform involved data processing operations on the data coming from different logging tools running at the same time, and to handle the large number of input/output operations required to make these measurements and to present the process data for plotting, the system has had to make compromises in the speed at which the logging of the well may progress. Other compromises include limiting the number of tools which can be run at one time, limiting the kinds of tools that may be combined for a given traverse through the well borehole, and so on. These compromises have all resulted in an increase in the cost and the time required to perform a plurality of well-logging operations on a given well.
Other disadvantages are presented by this single data bus-to-peripheral communication link and its attendant software overhead problems. A severe limitation in ease of configuration of the system, a severe limitation in the number of peripherals that can be added to the system, and no redundancy in communications with peripherals are examples of other disadvantages.
It would be advantageous, therefore, to provide a well-site data processing system which provides a back-up communications link from a back-up host processor to certain of the peripherals so that a failure of the host computer, or of its data bus, will not disable the entire system. It would also be advantageous to provide a well-logging data processing system having a communications controller to handle virtually all communications between the host computer and a plurality of peripheral units in which a comparatively few processor data bus cycles are required to move message data to and from the host computer memory, following which the host is freed for other tasks. It would also be advantageous to provide a data processing system in which communications between a host computer and its peripheral units are handled over a plurality of shared/sharable data paths which can be segmented, and the segment independently used for concurrent data transfers among several groups of the peripherals, thereby to increase the effective data transfer rate of the system.